The astronomical quintant is a navigation and measurement instrument used to determine latitude and longitude by calculating the angle between celestial objects and the horizon or between two celestial bodies. Its name derives from the fact that its arc spans one-fifth of a circle (or 72 degrees). This tool was essential for navigators and explorers during the 18th and 19th centuries, enabling more accurate and safer maritime voyages.

The quintant consists of a metallic framework, typically made of bronze or another corrosion-resistant material, with a graduated arc. It features a fixed mirror, a movable mirror attached to the index arm that slides along the arc, and a telescope or sighting device for aiming at the celestial object. The user aligns the telescope with the horizon while adjusting the movable mirror to make the image of the celestial body coincide with the horizon line, then reads the angle on the graduated arc.